Control unit for pinhole detectors



Oct. 13, 1953 w. E. COLEMAN CONTROL UNIT FOR PINHOLE DETECTORS 2Sheets-Sheet 1 Filed Feb. 27, 1952 INVENTOR WILLIAM E, COLEMAN ATTORNEYOct- 13, 1953 w E, O M 2,655,620

, CONTROL UNIT FOR PINHOLE DETECTORS Filed Feb. 27, 1952 2 Sheets-Sheet2 5 J 72 z; 65 id! 40, v 40 MP L dd I 616 46. 50am Inventor W/LL/flM(OLfMQ/M closely following the first hole.

Patented Oct. 13, 1953 FATENT OFFICE CONTROL UNIT FOR PINHOLE DETECTORSWilliam E. Coleman, Pleasant Hills Borough, Pa... assignor to UnitedStates Steel Corporation, a corporation of New Jersey ApplicationFebruary 27, 1952, Serial No. 273,697

14 Claims.

1 This invention relates to a control unit for pin hole detectors and isa continuation-in-part of my copending application, Serial No. 133, 3,dated December 16, 1949, now abandoned. It

pertains more particularly to such a device for detecting and-forcounting small holes in thin sheet products such as sheet steel which isused in the manufacture of tin cans. The control unit is used inconjunction with a strip marker and a throw-out device which throws theimperfect sheet from the line when it reaches a spot some distanceremoved from the inspection station. The control units in present userequire an appreciable time to permit proper operation of the throw-outdevice and the strip marker. During this period the control units areinsensitive to further impulses which may occur due to holes In a stripmoving 900 feet per minute, the operation should be fast enough to catchholes-l8 inches apart. This means that the detector unit should completeits cycle of operation in less than 0.10 second.

Conventional units will not do this so that some imperfect sheets passinspection. The control unit may also be used in conjunction with acounter to count the number of pin holes in a strip.

In my Patent No. 2,563,213, dated August 7,

v 1951, I have disclosed and claimed a device which is sensitive tofurther pulses which may occur when the control unit is operating tomark and throw out a defective sheet. While this device has proved to besuccessful in practice, it, like other conventional units, utilizesrelays which limit the speed of operation and which have moving contactswhich require frequent cleaning and adjustment.

It is an object of my invention to provide a control unit for a pin holedetector which will complete its operation in a very short period oftime and whichdoes not utilize relays or other parts which otherwiserequire frequent repair.

Another object is to provide a control unit which will amplify a shortimpulse into an impulse of sufllcient power and duration to operate anelectrical device such as a solenoid.

These and other objects will be more apparent after referring to thefollowing specification and attached drawings, in which:

Figure 1 is a schematic drawing showing a wirfled control unit.

the uncoiler 2 through side trimming knives 4' and measuring rolls 6 tothe shearing drums 8. where the strip is sheared into sheets S of thedesired length. .The sheared sheets pass over the conveyor It to adeflector [2 which is operated by means of a solenoid H to deflectimperfect sheets to a salvage piler IS. The perfect sheets pass over thedeflector [2 to a conveyor 18, which delivers the sheets to aprime sheetpiler 20. .A high intensity light source 22. is located above the stripadjacent the side trimming lmives 4 and a bank of light sensitivephotoelectric cells 24 is located in a shielded housinguhder the lightsources 22 below the strip. when a section of strip containing a holepasses between the light source 22 and photoelectric cells 24, lightpasses through the hole and strikes one or more of the photocells. pulsewhich is transmitted to a voltage amplifier 25 where the impulse isamplified to a value of sufiicient magnitude to operate the controls ofthe control unit 28. The pin hole detector may be of the type shown inthe patent to Chamberlin et al. No. 2,229,638. The control unit 28converts the short impulse from the amplifier 26 into an impulse ofsufficient power and duration to operate a solenoid 3 of a strip marker32 which places a visible mark next to the hole, thus identifying thesection ofstrip containing the hole. The control unit also provides animpulse to energize a solenoid in a proportional timer 34 which isdriven by a motor 36 which also drives the measuring rolls 6. Thus thetimer 34 is in synchronism with the movement of the strip. Theproportional timer 34 is preferably of the type shown in the patent toLadrach No. 2,217,342 and is equipped with a contact mechanism whichenergizes the solenoid hi to tilt the deflector l2 upwardly and directthe sheet containing the pin hole downwardly into the salvage piler l6.If desired, the control unit 28 may also be used to pro- This generatesa small voltage im- 4 is connected to the positive terminal of a directcurrent source 5%.. The cathode 380 is connected to the negativeterminal of the power source 50 through a resistance 52. The tube 38connected to the resistors 48 and 52 and D. C. power source 58 acts asan impedance reducing circuit which tends to stabilize the overallsystem by providing a certain amount of isolation between the amplifier28 and the balance of the control circuit. While this impedance reducingcircuit may be dispensed with, it is important in making the controlunit commercially successful. The positive terminal of power source 58is connected to the plate 4GP through a resistance 54 and the negativeterminal of power 'source 50 is connected. to the cathode 48C through aresistance 58. A capacitor 58 is arranged in parallel with theresistance 56. 38 is developed across resistor 52 and is transmitted toa resistor 60 and the grid 48G through a capacitor 62. The resistor 58and capacitor 58 limit the normal current flowing through tube 46. Abattery or other D. C. power source could be substituted for theresistor 56 and capacitor 58. This battery could be installed in thecircuit of cathode 48C in place of the resistor 58 and capacitor 58 withits positive terminal connected to the cathode, or it could be installedbetween the resistor 68 and the line from the negative terminal of D. C.power source 58. In the latter case, the negative terminal of thebattery will be connected to the resistor 80. Tube 48 together withresistors 54, 58 and 88, capacitor 58 and constant voltage D. C. powersource 58 act as an amplifier circuit which amplifies the pulse fromtube 38 and also reverses its polarity. If the impulse is of suflicientmagnitude this circuit could be omitted, in which case the capacitor 82will be connected to the grid 44G. The positive terminal of D. C. powersource 58 is connected to the grid 42G through a resistor 84 and itsnegative terminal is connected to the cathode 42C through a resistrr 86.The plate 42F is connected to the positive terminal of D. C. powersource 58 throu h a resistor 68. A capacitor is connected in the linebetween resistors 64 and 54. The positive terminal of D. C. power sourceis connected to the plate MP through a resistor i2 and the negativeterminal is connected to the cathode 440 through resistor 86. The grid44G is connected to the D. C. power source 59 through a voltage dividerconsisting of resistors 74 and 18. The grid 44G will therefore besufficiently negative with respect to cathode 440 that tube 44 will benormally non-conducting. A capacitor 78 is provided in the line betweenresistor 12 and grid 42G.

A tap 88 from the plate 42P leads through a capacitor 82 to the grids84G and 86G of grid controlled gasrectifier tubes 84 and 88. If de--sired, the tap 88 might be taken from the grid 446-, but it is notpreferred to do so. A resistor 88 is installed in the line between grid84G and capacitor 82 and a similar resistor 90 is installed in the linebetween grid 86G and capacitor 82.;

The output pulse from tube The operation of the device is as follows:When a hole is detected by means of a voltage generating device such asthe electric eye 24 the impulse created thereby is amplified in theamplifier 26 and is impressed on the grid 38G. The tube 38 is normallypartially conducting but when the positive impulse is impressed on itsgrid 38G, the current flowing through the tube is increased, thuscausing a rise in the voltage across resistor 52, which voltage rise istransmitted to the grid 486 through the capacitor 62. The tube 40 isalso normally partially conducting but the positive impulse on its gridincreases the conduction thereof. The pulse is transmitted as a negativepulse from the plate 48F through capacitor 10 to the grid 42G of tube 42which is normally conducting. This normal current in tube 42 developsavoltage drop across resistor 66 which makes the cathode 44C positivewith respect to the negative side of the power source 50. When the neg-ative pulse appears on grid 42G it reduces the current through tube 42,which in turn lowers the voltage drop across resistor 88 and lowers thepotential of cathode 44C sufliciently to permit conduction to start intube 44. This current flows from power source 50 through resistor 12 andthe voltage drop thus occurring across resistor '12 causes the plate 44Fto drop in potential. This drop in potential is transmitted throughcapacitor 18 back to grid 42G, thus further reducing its potential. Thisaction is cumu- Iative and instantaneous and drives the voltage of grid42G with respect to cathode 42C well beyond the current cut-off point oftube 42. The cumulative action stops when'the current in tube 44 can no"longer increase due to saturation in tube 44 at which time capacitor [8begins to discharge through resistors 12 and 84, thus permitting thepotential 01 grid 42G to increase at a rate determined by the values ofcapacitor 18 and resistors '12 and 64. When the tube 42 is cut an thepotential of'plate 421 suddenly increases and remains high-as long asthe tube is cut off. Thus a relatively long positive impulse is producedat plate 42? in place of the short negative impulse at grid 42G. Thisimpulse is transmitted through capacitor 82 and resistors 88 and to thegrids 84G and 88G, respectively. The positive impulse fires tubes 84 and88 and permits current from the A. C. power source 98 to pass throughthe tubes and energize marker solenoid 38 and the solenoid inproportional timer 34. When the potential of grid 42G reaches the levelwhereconduction starts in tube 42 the cumulative actions mentioned aboveare reversed so that the tube 42 becomes conducting and the tube 44non-conducting. This permits the tubes 84 and 88 to cease conducting andthe circuit is again ready for a new impulse. In case the solenoid 30and the solenoid or timer 34 were normally energized and would completea circuit when deenergized, a negative impulse could be used to triggertubes 84 and 86. In this case, D. C. power source 92 could be omitted.

In brief, it. is seen that a short. positive p se of as little as .001second in duration or less from the amplifier 26 is amplified andinverted in tube 48 and is again inverted and converted to a longerpulse of about .10 second in tubes 42 and 44. This longer impulse istransmitted to tubes 84 and 88, which conduct long enough to. operatethe solenoids oi the timer and marker.

Figure 2 shows a somewhat simplified embodiment of my invention in whichthe impedance reducing circuit and one of the gas tubes. are

omitted. In this embodiment the same reference numerals are used as inFigure 1 to indicate like elements. The grid 40G and the cathode 400 areconnected to the amplifier 26 as shown. The connection to the cathode isprovided with a bias source I00 such as a battery. The plate MP isdirectly connected to the plate MP. The negative side of D. C. powersource 50 is connected to the grid 44G through a connection I 02. Meanssuch as a battery I04 is provided in the connection I02 for the purposeof maintaining the grid 44G normally positive with respect to thenegative side of the D. C. power source 50. The plate 42F is connectedto the grid MG and the cathode 84C is connected to thepositive side ofD. C. power source 50. One side of the A. C. power source 96 isconnected to the cathode 84C and the other side is connected through anelectrical device 98 to the plate 841?. The electrical device 98 may bethe solenoid of a counter, marker or timer. The operation of thiscircuit is substantially the same as that of Figure 1. If the electricaldevice 98 is a counter it will count the number of pin holes occurringin the sheet S.

While two embodiments of my invention have been shown and described itwill be apparent that other adaptations and modifications may be madewithout departing from the scope of the following claims.

I claim:

1. A control unit for a pin hole detector having detecting means forgenerating a voltage impulse when a pin hole occurs in a sheet, a timerand means responsive to actuation of the timer for classifying thesheets; said control unit comprising a pair of vacuum tubes each havinga grid, cathode and plate, means including a capacitor for connectingthe grid of the first of said tubes to the plate of the second of saidtubes, a D. C. power source, a direct current connection between thepositive side of said power source and the grid of the second tube, adirect current connection between the negative side of said power sourceand the grid of the second tube, a

resistor in each of said last named connections providing a voltagedivider, a connection between the cathodes of said tubes, a connectionbetween said last named connection and the ne ative side of said D. C.power source, a resistor in said last named connection, connectionsbetween the positive terminal of said power source and the plates ofeach of said tubes, a resistor in each of the last named connections. adirect current connection between the positive terminal of said powersource and the grid of the first tube, a resistor in the last namedconnection, means for connecting the detecting means to one of saidgrids, a grid controlled gas rectifier tube having a grid, cathode, andplate;-

means including a capacitor for connecting the grid of said gas tube tothe plate of one of the pair of tubes, an A. C. power source having oneterminal connected to the cathode of said gas tube and the otherterminal connected to one 6 pacitor for connecting the grid of the firstof said tubes to the plate or the second of said tubes, 9. D. C. powersource, a direct current connection between the positive side of saidpower source and the grid of the second tube, a direct currentconnection between the negative side of said power source and the gridof the second tube, a resistor in each of said last named connectionsproviding a voltage divider, a connection between the cathodes of saidtubes, a connection between said last last named connection and thenegative side of said D. C. power source, a resistor in said last namedconnection, connections between the positive terminal of said powersource and the plates of each of said tubes, a resistor in each of thelast named connections, a direct current connection between the positiveterminal of said power source and the grid of the first tube, a resistorin the last named connection, means for connecting the detecting meansto one of saidgrids, :a grid controlled rectifier 'tube having a grid,cathode, and plate, means for connecting the grid of said rectifier tubeto the plate of one or the pair of tubes, means for maintaining the gridof said rectifier tube nor mally negative with respect to its cathode,an A. C. power source having one terminal connected to the-cathode ofsaid rectifier tube and the other terminal connected to one side of thetimer, and a connection between the other side or the timer and theplate of the rectifier tube.

3. A control unit according to claim 2 having a secondgrid controlledrectifier tube, means connecting the grid of said second rectifier tubeto the connection to the grid of the first rectifier tube, meansconnecting the cathode of the second rectifier-tube to one terminal ofthe A. C. power source, means for connecting the other termianl of theA. C. power source to the plate of the second rectifier tube, and asolenoid in said last named connection.

4. A control unit according to claim 2 in which the means for connectingthe voltage generating means to one of said grids includes a thirdvacuum tube having a grid, cathode and plate, means for connecting thevoltage generating means to the gr'idof said third tube, and means forconnecting the D. C. power source to the cathode and plate of the thirdtube.

5. A control unit according to claim 4 having a second grid controlledrectifier tube, means connecting the grid of said second rectifier tubeto the connection to the grid of the first rectifier tube, meansconnecting the cathode of the secnd rectifier tube to one terminal ofthe A. C. power source, means for connecting the other terminal of theA. C. power source to the plate of the second rectifier tube, and asolenoid in said last named connection.

6. A control unit for a pin hole detector hav. ing detecting'means forgenerating a voltage impulse when a pin hole occurs in a sheet, a timerand means responsive to actuation of the timer for classifying thesheets; said control unit comprising a vacuum'tube having a grid,cathode and plate, means including a capacitor and resistor forconnecting the detecting means to said grid, 8. direct current powersource, means for connecting the direct current power source to saidcathode and plate, a resistance in the connection between said powersource and said cathode, a second vacuum tube having a grid, cathode andplate, a connection between the cathode of the first tube and the gridof the second tube, a capacitor in said last named connection, a con- 7motion betwe n the ri of thezs ond'tube' an the negative sid o sa d 1 0.powe ource. is resis or in said la named c nnectio m an or connec n onmi al 't e D.- Qrowo s urce to th second name p ate. a re s or in saidlast named connecting means, means fior connecting the other terminal ofthe D. C. power source to the second named cathode, means for limitingthe normal amount of current flowing in the second tube, a third vacuum'tube having a grid, cathode and plate, means including a capacitor forconnecting the plate ofthe secand tube to the grid of the third tube, aconnection between the positive terminal of said D. C. power source andthe grid and plate of the third tube, a resistor in each of the lastnamed connections, a fourth vacuum-tube having a grid, cathode andplate, a connection between the cathodes of said third and fourth tubes,a corir ection between said last named connection nd the negative sideof said D. C. power source, a resistor in said last named connection, adirect current connection between the positive side of said power sourceand the grid of the-fourth tube, a direct current connection between thenegative side of said power source and the grid of the fourth tube, aresistor in each of said last named connections providing avoltagedivider, a connection between the positive terminal of said D. C. powersource and the plate of the fourth tube, a resistor in said last namedconnection, a connection including a capacitor between the grid of thethird tube and the plate of the fourth tube, a grid controlled rectifiertube having a grid, cathode and plate, means Ior maintaining the grid ofthe rectifier tube nega tive with respect to its cathode, means forconnecting the plate of the third tube to the grid of the rectifiertube, an A. C. power source having one terminal connected to the cathodeof said rectifier tube and the other terminal connected to one side ofthe timer, and a connection between the other side of the timer and theplate of the rectifier tube.

7. A control unit according to claim 6 having a second grid controlledrectifier tube, means connecting the grid of said second rectifier tubeto the connection to the grid of the first rectifier tube, meansconnecting the cathode of the secand rectifier tube to one terminal ofthe A. C. power source, means for connecting the other terminal of theA. C. power source to the plate of the second rectifier tube, and asolenoid in said last named connection.

8. A control unit for energizing an electrical device in response to animpulse from a voltage generating means comprising a pair of vacuumtub-es each having a grid, cathode and plate, means including acapacitor for connecting the grid of the first of said tubes to theplate of the second of said tubes, 3. D. C. power source, a connectionbetween the negative side of said power source and the grid of thesecond tube,

means in said connection for maintaining the grid of said second tubenormally positive with respect to the negative side of said powersource, a connection between the cathodes of said tubes, a connectionbetween said last named connection and the negative side of said D. C.power source, a resistor in said last named connection, connectionsbetween the positive terminal of said power source and the plates ofeach of said tubes, a resistor in each of the last named connecvtions, adirect current-connection between the positive terminal of said powersource and the,

grid of the first tube, a resistor in the last named connection, meansfor connecting said voltage generating means to one of said grids, agrid controlled rectifier tube having a grid, cathode and plate, meansfor connecting the grid of said rectifier tube to the plate of one ofthe pair of tubes, means for maintaining the grid of said rectifier tubenormally negative with respect-to its cathode, an A. C, power sourcehaving one terminal connected to the cathode of said rectifier tube andthe other terminal connected to one side of the electrical device, and aconnec- .tion between the other side of the electrical device and theplate of the rectifier tube.

.A c ntrol un t according to claim .8 having a second grid controlledrectifier tube, means co ne t n the ri o said sec nd r t fi tu to theconnection to the grid of the first rectifie tube. me n c nn i g t ca hoe o h second rectifier tube to one terminal of the A. C.

p er sourc m ns for. c nn ctin the t e te minal or the A. .0. powersource to the plate ing a second grid controlled rectifier tube, meansconnecting the grid of said second rectifier tube to the connection tothe grid of the first rectifier tube, means connecting the cathode ofthe second rectifier tuoe to one terminal of the A. C.

power source,'means for connecting the other terminal of the A. 0. powersource to the plate of the second rectifier-tube, and a solenoid in saidlast named connection.

' 12. A control unit for energizing an electrical device in responseto'an impulse from a voltage generating means comprising a vacuum tubehav ing a grid, cathode and plate, means including a capacitor andresistor for connecting the voltage generating means'to said grid, adirect current power source, means for connecting the direct currentpower source to said cathode and plate, a resistance in the connectionbetween said power source and said cathode, a second vacuum tube havinga grid, cathode and plate, a connection between the cathode of the firsttube and the ,grid of the second tube, a capacitor in said last namedconnection, a connection between the grid of the second tube and thenegative side of said D. C. power source, a resistor in said last namedconnection, means for connecting one terminal of the D. C. power sourceto the sec ond named plate a resistor in said last named connectingmeans, means for connecting the other terminal of the D. C. power sourceto the secand named cathode, means for limiting the normal amount ofcurrent flowing in the second tube,

a hi d vacuum u e h v n a i cathode an plate. means includin a cap cit ror Connecting the plate of the second tube to the grid of the thirdtube, a connection between the positive terminal of said D. C. powersource and the .grid and plate of the third tube, a resistor in each ofthe last named connections, .a fourth vacuum tube having a grid, cathodeand plate,

a connection between the cathodes of said third and fourth vacuum tn esaconnection betwee said last named connection and the negative side ofsaid D. C. power source, a resistor in said last named connection, adirect current connection between the positive side of said power sourceand the grid of the fourth tube, a direct current connection between thenegative side of said power source and the grid of the fourth tube, aresistor in each of said last named connections providing a voltagedivider, a connection between the positive terminal of said D. C. powersource and the plate of the fourth tube, a resistor in said last namedconnection, a connection including a capacitor between the grid of thethird tube and the plate of the fourth tube, a grid controlled rectifiertube having a grid, cathode and plate, means for maintaining the grid ofthe rectifier tube negative with respect to its cathode, means forconnecting the plate of the third tube to the grid of the rectifiertube, an A. C.' power source having one terminal connected to thecathode of said gas tube and the other terminal connected to one side ofthe electrical device, and a connection between the other side of theelectrical device and the plate of the rectifier tube.

13. A control unit according to claim 12 having a second grid controlledrectifier tube, means connecting the grid of said second rectifier tubeto the connection to the grid of the first rectifier tube, meansconnecting the cathode of' the second rectifier tube to one terminal ofthe A. C. power source, means for connectingthe other terminal of the A.C. power source to the plate of the second rectifier tube, and asolenoid in said last name'd connection.

14. A control unit for a pin hole detector having detecting means forgenerating a voltage impulse when a pin hole occurs in a sheet, a timer.

and means responsive to actuation of the timer for classifying thesheets; said control unit comprising a pair of vacuum tubes each havinga grid, cathode and plate, means including a capacitor for connectingthe grid of the first of said tubes to the plate of the second of saidtubes, a D. C. power source, a. direct current connection between thepositive side of the power source and the grid of the second tube, adirect current connection between the negative side of said power sourceand the grid of the second tube, a resistor in each of said last namedconnections providing a voltage divider, a connection between thecathodes of said tubes, a con nection between said last named connectionand the negative side of said D. C. power source, a resistor in saidlast named connection, connections between the positive terminal of saidpower source and the plates of each of said tubes, a resistor in each ofthe last named connections, a direct current connection between thepositive terminal of said power source and the grid of the first tube, aresistor in the last named connection, means including a third vacuumtube for connecting the detecting means to one of said grids, said thirdvacuum tube having a grid, cathode and plate, means for connecting saidvoltage generating means to the grid of said third tube, means forconnecting the D. C. power source to the cathode and plate of the thirdtube, a grid controlled rectifier tube having a grid, cathode, andplate, means for connecting the grid of said rectifier tube to the plateof one of the pair of tubes, means for maintaining the grid of saidrectifier tube normally negative with respect to its cathode, an A. C.power source having one terminal connected to the cathode of saidrectifier tube and the other terminal connected to one side of thetimer, and a connection between the other side of the timer and theplate of the rectifier tube.

